Glaucoma is the second leading cause of blindness worldwide. In the United States, approximately 2.5 million Americans are affected by this potentially blinding eye disease. Optical coherence tomography (OCT) is a non-invasive imaging technique allowing high-resolution cross-sectional imaging of the human retina. Under the previous grant period, we have developed an OCT system that outperforms existing commercially available systems by orders of magnitude, enabling video rate cross-sectional and 3-dimensional volumetric imaging of the human retina in vivo. Since glaucoma causes optic nerve head (ONH) cupping and retinal nerve fiber layer (RNFL) thinning prior to loss of vision, optical coherence tomography (which measures both ONH structure and nerve fiber layer thickness) could enable early detection of glaucoma prior to permanent loss of vision. This earlier detection would enable earlier treatment to prevent permanent loss of vision. Since glaucoma also causes progressive ONH changes and nerve fiber layer thinning prior to further loss of vision, optical coherence tomography could enable earlier detection of glaucomatous progression prior to further permanent loss of vision, enabling more aggressive preventive treatment. Current clinical techniques only allow diagnosis of glaucomatous loss of vision after up to half of the retinal ganglion cells are permanently lost. In this grant period we propose to evaluate various methods to analyze the ONH and RNFL thickness in a population of 100 glaucoma patients and 50 ocular hypertension patients and determine characteristic features associated with glaucoma in RNFL thickness maps centered on the ONH. The characteristic features will be correlated with standard technologies to evaluate glaucoma. Patients will be imaged at enrollment in the study and at one year follow up. We will determine the reliability and reproducibility of ONH parameters and RNFL thickness determinations. The results of this study will quantify the changes in the ONH and RNFL that can be detected by our OCT system and will provide the necessary framework for a large multi-center longitudinal trial which would evaluate if OCT's detection of ONH and nerve fiber layer changes can precede current clinical techniques' (i.e. GDx, HRT, OCT3, Humphrey visual field, etc) detection of glaucoma and vision loss. [unreadable] [unreadable] [unreadable]